Heating furnace control



0a. 11, 1932. R. w. S T EM ,8

HEATING FURNACE CONTROL Filed Sept. 6, 1930 Paws/P L/A/E INVENTORfiusJe// #4 Jfgm BY fi fiw, Maw

ATTORNEY-5 Patented Oct. 11, 1932 UNITED STATES PATENT" OFFICE RUSSELLW. STEl I, O1? BETHLEHEM, PENNSYLVANIA, ASSIGNOB TO PENN ELECTRICSWI'IGE 00., 0F DES MOINES, IOWA m'rme rurmaon con'rnon Application andSeptember a, 1930. Serial No. 480,045. I

This invention relates to improvements in the thermostatic control offurnaces used for heating houses, oflices, shops, other buildings andthe like in which motor driven means are used for effecting combustionof fuel, as in burning coal or coke with motor driven forced or induceddraft fans and as in burning oil with motor driven burners. Theinvention is of special value and application in connection with the useof solid fuels such as coal and coke but it also has certain advantagesin the burning of liquid fuels such as oil. T

' In conventional practice a thermostat actuated' by the temperature inthe enclosed space to be heated arranged to start the operation of suchmotor driven means when the temperature in this-space falls below a.

predetermined mi imum limit and to stop such motor driven means when thetemperature in this space rises above a predetermined maximum limit.While the results so obtained are fairly satisfactory with respect tocontrol of the temperature in the enclosed space to behea'ted, withinthe limits of the thermostats used, this I ractice disregards severalelements essential to eflicient operation of the heating furnace. Withthe usual heating furnacethermal efficiencies fall oif rapidly if thetemperature of the waste gases escaping through the stackflue exceeds amaximum limit characteristic of the par- :ticular heating furnace, andthe same is true when the temperature in the fire-box falls below aminimum limit also characteristic but to a lesser extent of theparticular furnace. From the standpoint of efliciency,-the temperatureof the waste gases escaping through the stack flue is much moresignificant than are the limits within which temperature may bemaintained in-the enclosed space to be heated. I

The present invention provides for the I superposlng, in a particularlyadvantageous manner, of control effected by themostatic means responsiveto the temperature in the stack flue upon control effected bthermostatic means arranged in the usua manner. Sevesal importantadvantages are thus secure The invention will be further described inconnection withthe accompanying drawing which illustrates,diagrammatically and conventionally, an embodiment of the invention. Itis intended and will be understood that the accompanying drawing isintended merely to illustrate the invention and that it is not to beinterpreted in any limiting sense.

The accompanying drawing illustrates a heating furnace 1 comprising theusual firebox in which fuel is burned, heat transferring surfaces overwhich the hot products of combustion from" the hot fire-box pass for thetransfer of heat to the heating medium, air, Water or steam for exam le,used in the heating system,-and a stack ue 2 through which the hot gasesfrom the fire-box which have passed over the heat transferring surfacesescape. The motor of a motor driven means for effecting combustion offuel in the firebox is shown at, 3. The means shown comprise a fanarranged to provide forced draft through a grate on which coal or coke,for example, is burned. Instead of such a forced draft fan, an induceddraft fan may be positioned in the stack fiue. Or an oil burner,

for example, may be arranged, generally with respect. to the heatingfurnace, as shown in cuit to the motor when the temperature in the stackflue falls below the predetermined minimum limit independently of theoperation of the thermostat 4. That is, the thermostat 5 is adapted toclose the power circuit.

to the motor 3 whenever the temperature in the stack'flue 2 fallsbelow apredetermined minimum limit even though the thermostat 4 is operating,to maintain the power circuit to the motor 3 opened at the time. Athermostat ,6 is advantageously arranged in juxtaposition to the stackflue 2, this thermostat 7 being adapted to open the power circuit toabove the predetermined maximum limit even though the thermostat 4 maybe operating to maintain this power circuit closed at the time. Certainadvantages of the invention may be obtained even though the thermostat 6be omitted, as noted below, the circuit to the thermostat 4 in such casebeing completed as indicated at 7. Although the thermostats 4, 5 and 6are shown in the accompanying drawing as connected directly in the powercircuit, more clearly to illustrate the invention, it will be understoodthat these thermostats may be arranged to open and close the powercircuit through a suitable relay as indicated at 8.

The temperatures at which the several thermostats are adjusted tooperate may be varied widely to meet the varying requirements ofdifferent situations, For example, the thermostat 4 may be adjusted toclose-the power circuit'at a temperature of 68 F. and to open the powercircuit at a temperature of 70 F the thermostat 5 may be adjusted toclose the power circuit at a temperature of 200-300 F. and thethermostat 6 may be adjusted to open the power circuit at a temperatureof 7 50900 F. It will be obvious that thermostat 4 may be adjusted tomaintain a higher or a lower temperature in the space to beheated. Asthe heat transferring efiiciency of the furnace decreases, the optimumvalue of the minimum temperature limit at which the thermostat 5 isadjusted to operate usually increases; it may exceed 600 F some cases. Amaximum temperature limit at which the thermostat 6 is adjusted tooperate may be fixed with reference to safety or it may be fixed at alower value for the purpose of maintaining more efiicient furnaceconditions.

As applied in conjunction with heating furnaces using solid fuel orliquid fuel, the

invention improves the efficiency of the heating furnace by avoidinglosses incident to too low fire-box temperatures and to too high stackflue temperatures, avoids excessive stack flue temperatures and assistsin the maintenance of more uniform temperatures in the space to beheated. As applied in conjunction with heating furnaces using solidfuel, the invention also avoids objectionable clinker-ing, by limitationof maxi mum temperatures, and reduces the danger of fire-box explosionsincident to the formation of combustible gases at fire-box temperatureshigh enough to cause the formation of such gases but not high enough tocause their continuous ignition as formed.

If the thermostat 6 be omitted, the advantages of the invention involvedin limitation of the maximum stack flue temperature are lost but thoseadvantages involved in the maintenance of the minimum stack flue tembringing the space to be heated to an increased temperature, followmgsuch tlme adjustment, more quickly; in some cases such acceleratedrecovery of a higher temperature is more important than the improvementin eiiiciency to be accomplished by limitation of the maximum stack fluetemperature. I

It will be understood that independent thermostatic elements may be usedin the thermostat 4 to effect the opening and to effect the closing ofthe power circuit thereby and that a single thermostatic element may beused to effect the closing of the power circuit by the thermostat 5 andto effect the opening of the power circuit by the thermo-- stat 6.

Having described my invention, I claim 1. In combination, a heatingfurnace comprising a fire-box in which fuel is burned, heat transferringsurfaces over which the hot products of combustion from the fire-boxpass and a stack \flue through which the hot gases from the fire-boxescape after passing over the heat transferring surfaces, and motordriven means for effecting combustion of fuel in said fire-box, and apower circuit adapted to supply operating power to said motor drivenmeans, and a thermostat actuated'by the temperature in an enclosed spaceto be heated adapted to close said power circuit when the temperature insaid space falls below a predetermined minimum and to open it when thetemperature therein rises above a predetermined maximum, and athermostat actuated by the temperature in said stack flue adapted toclose said power circuit when the temperature in said stack flue fallsbelow a predetermined minimum independently of the operation of saidfirst mentioned thermostat, and a thermostat actuated by the temperaturein said stack flue adapted to open saidpower circuit when thetemperature in said stack flue rises above a predetermined maximum.

2. In combination, a heating furnace comprising a fire-box in which fuelis burned, heat transferring surfaces over which the hot products ofcombustion from the fire-box pass and a stack flue through which the hotgases from the fire-box escape after passing over in =aid fire-box, anda power circuit adapted to supply opera-ting power to said motor drivenmeans, and thermostatic means actuated by the temperature in an enclosedspace to be heated adapted to close said power circuit when thetemperature in said space falls below a predetermined minimum and toopen said power circuit when the temperature in said space rises above apredetermined maximum, and thermostatic means actuated by thetemperature in said stack flue adapted to close said power circuit whenthe temperaturein sa-idvstack flue falls below a predetermined minimumeven though said first mentioned 35 thermostatic means are at the timeoperating to open said power circuit and adapted to open said powercircuit when the temperature in said stack flue rises above apredetermined maximum even though said first mentioned thermostaticmeans are at the time operating to, close said power circuit.

3. A stoker control system comprising a motor, a room thermostat, and athermal controlled stack-switch,all wired in series in a power circuitto control the operation of said 1 motor cooperatively relative to theroom temperature and stack temperature, and means controlled by saidstack temperature. to shunt said room thermostat and operate said motorat a predetermined low stack temperature and independent of said roomtemperature.

4. A stoker control apparatus including a stoker operating motor and theusual furnace stack, a low limit switch and a high limit :4 switchcontrolled by stack temperature, a

room' thermostat, and electrical connections by means of which the lowlimit switch at low limit temperature dominates motor ener-- gization,and by means of which at other tem- 40 peratures the thermostat and highlimit switch can initiate motor energization.

5. A stoker control apparatus including o a stoker operating motorandthe usual furnace stack, a lowjlimit switch and a high limit switchcontrolled by stack temperatures,

a room thermostat, and electrical connections by means of which the lowlimit switch at low limit tem rature dominates motor energizetion, andy'meansof which attemperatu'resbetween highand. low limits thethermostat andhigh limit switch can initiate motor energization. I v

In testimony whereof I aflix m si ature. RUSSELL S EM.

